Is this good for your city? For your health? (Photo credit: Richard Masoner / Cyclelicious)

In response to a comment in my last post, I’d like to discuss further how cities could affect transportation mode share,

particularly as it concerns driving. In the U.S., every single city has a dominant auto share (drive alone and carpool) except for New York, Washington D.C., Boston and San Francisco. In Chicago, where I live, the auto mode share is 61%. In the Chicago metro area, it’s 71%. So why is this a big deal? Why should urban policy be oriented towards reducing auto mode share?

It’s one way of efficiently managing an urban transportation system, for one. It also helps to deal with the following economic, social and environmental factors (externalities) associated with auto travel:

Rising facility costs. The costs of expanding highways and parking facilities is increasing. In many cases it is more cost-effective to manage demand than to continue expanding supply.

Increased urbanization. In most developed countries the majority (typically 80-90%) of people and jobs are located in urban areas, where traffic and parking problems are significant and alternative modes are cost-effective.

Demographics. The population is aging in most developed countries, increasing the importance of providing quality travel options for non-drivers.

Energy Costs. Vehicle fuel costs are projected to increase in the future due to depletion of oil supplies and environmental constraints.

Consumer preferences and market trends. Many consumers want to live in more multi-modal communities where it is possible to walk and bicycle safely, use neighborhood services, and have access to quality public transportation.

Environmental concerns. Concerns over air pollution, sprawl and other environmental impacts are motivating policy changes to encourage more efficient transportation.

In the context of the previous post, my skepticism towards traffic signal prioritization (TSP) is rooted in the rising facility costs and environmental concerns categories, although, all of these points can and should be applied. In cities where land is at a premium, we simply cannot afford to appropriate more land for the building of roads. And traffic signal prioritization, while making traffic move more efficiently in the short-term creates induced demand in the long-term. And then we are back to the original problem that traffic signal prioritization was trying to solve.

The environmental concerns, particularly concerning air quality in large cities is a serious concern that I addressed. Induced demand, which causes an increase in vehicle miles traveled, exacerbates air quality and emissions issues. There is a reason that most large U.S. cities are eligible for CMAQ grants. Those grants should not be used in TSP.

There are a variety of solutions (incentives) that cities could use to reduce auto mode share and shift towards alternative modes. For more information, see here.